The present invention relates generally to a micro-mechanical device for steering and manipulating beams of light, and in particular, to a gimbaled micro-mirror positionable by one or more thermal actuators.
Beam steering devices are found in a variety of products, including laser bar scanners, CD-ROM heads, laser printers, optical switches, robotic vision scanners, optical choppers, optical modulators, and display devices. Many micro-mirrors are designed using any one (or combination) of only three primary styles of operation. First, the xe2x80x9cphase-onlyxe2x80x9d piston-style device, known as the flexure-beam micro-mirror, operates such that the motion of the reflective surface is along an axis orthogonal to its plane. The reflective mirror surface is attached to several identical flexures that support the mirror uniformly around its perimeter. As a result the direction of propagation is preserved and only the phase is modified by lengthening or shortening the optical path of the incident light.
The second design is a cantilever micro-mirror that is probably the most common style. The mirror of this device is attached at one end by as little as a single flexure or hinge and is deflected upward or downward at an angle as the device is actuated. This device alters the direction of propagation of an incident beam of light and also creates a non-uniform phase-front in the reflected light due to the slanting of the mirror surface.
The third design is the torsion-beam micro-mirror that is similar to the cantilever device with the exception that the mirror is attached by two flexures or hinges opposite each other. As a result, this device rotates along the longitudinal axis defined by these flexures. The mirror surface tilts as with the cantilever device, but it can be tilted in two directions along both sides of the flexures rather than just one. These mirrors are typically limited in movement to one or two directions. There is need and market for micro-mirrors that have sufficient multi-movement capability as to overcome the above prior art shortcomings.
Coupling actuators with micro-mirrors allows for moving these devices out of the plane of the substrate to steer the light beam. Various types of actuators, including electrostatic, piezoelectric, thermal and magnetic have been used for this purpose. For example, U.S. Pat. No. 6,028,689 (Michalicek et al.) discloses a multi-motion micro-mirror manipulated by electrostatic potential.
A device with a micro-mirror, four thermal actuators and four torsion bars that connect the mirror and the actuator is described by Chiou et al. in xe2x80x9cA Micromirror Device with Tilt and Piston Motionsxe2x80x9d, v.3893, SPIE, pp.298-303 (1999). Attaching the actuators to the micro-mirror can reduce the range of motion.
What is needed is a faster, more precise and compact apparatus for steering beams of light.
The present invention relates generally to a micro-mechanical device for steering beams of light. The micro-mechanical device includes a gimbaled micro-mirror with a mirror mechanically coupled to the surface of the substrate by one or more gimbals. The thermal actuators are positioned to engage with, but are not attached to, the mirror. The gimbaled micro-mirror is positionable by a plurality of thermal actuators through two or more degrees of freedom. The micro-mirror is typically positionable through pitch, roll and lift.
The thermal actuators are capable of repeatable and rapid movement of the micro-mirror to steer a beam of light. The present gimbaled micro-mirror has an extremely small mass and high frequency response while at the same time exhibiting high tolerance to vibration noise. The micro-mechanical device of the present invention has many uses related to optical switching including beam steering, shaping and scanning or projection applications, as well as for optical communication.
In one embodiment, the micro-mechanical device for steering beams of light comprises at least one mirror constructed on a surface of the substrate. At least one gimbal mechanically couples the mirror to the surface of the substrate in a neutral position. At least one thermal actuator is constructed on the surface of the substrate adjacent to the mirror. The thermal actuator has a free end positioned to engage the mirror, but is not attached to the mirror. The thermal actuator is adapted to move the mirror out of the neutral position. The neutral position is typically an in-plane configuration. The mirror is typically in an out-of-plane configuration when the thermal actuators are in an activated position.
In one embodiment, two or more thermal actuators are adapted to move the mirror through at least two degrees of freedom relative to the surface of the substrate. In some embodiments, the gimbal suspends the mirror over the surface of the substrate.
In one embodiment, the free end slides along a lower surface of the mirror during movement between the unactivated position and the activated position. In another embodiment, the mirror can include a plurality of outriggers positioned to mechanically engage with the free ends of the thermal actuators.
The mirror may optionally include a plurality of supports extending distally from a perimeter of the mirror. A plurality of pads attached to the supports are positioned to engage with the surface of the substrate when the thermal actuators are in an unactivated position. The pads may optionally be located on the surface of the substrate. Alternatively, the pads operate as end-stops when the thermal actuators are in an activated position.
In one embodiment, the mirror is rectangular and at least one thermal actuator is located at each corner thereof The gimbal may optionally include at least one first arm extending distally from the mirror, a member attached to a distal end of the first arm, and a second arm extending from the member to an anchor on the surface of the substrate. In one embodiment, the first arm is perpendicular to the mirror. In another embodiment, the first arm is parallel to the second arm.
The thermal actuator typically includes at least one hot arm having a first end anchored to the surface and a distal end located above the surface. A cold arm having a first end is anchored to the surface and a distal end. The cold arm is located above the hot arm relative to the surface. A member is mechanically and electrically coupling the distal ends of the hot and cold arms. The member includes a free end configured to engage with the mirror The mirror is moved when current is applied to at least the hot arm. An array of mirrors can be constructed on the surface of the substrate.
The present invention is also directed to an optical switch comprising at least one input optical fiber and one or more output optical fibers. The present micro-mechanical device for steering beams of light is positioned to selectively direct an optical signal projecting from the input optical fiber to any of the output optical fibers.